In vitro clonal assays for hematopoietic progenitor cells will be employed to study the interaction of regulatory proteins and growth and developmental agents with hematopoietic progenitor cells. Specifically, the mechanism by which phorbol esters differentially affect various hematopoietic progenitor cells will be studied. The influence of alcohol and its metabolites on hematopoietic cell proliferation and differentiation will be examined. Finally, the effect of immobilization of erythropoietin on the interaction of the hormone and its target cells will be investigated